Optical Combiner Apparatus

ABSTRACT

Optical combiners are provided. The optical combiner may have a see through optically transparent substrate and a patterned region included in the optically transparent substrate and disposed along a wave propagation axis of the substrate. The patterned region may be partially optically reflective and partially optically transparent. The patterned region may comprise a plurality of optically transparent regions of the optically transparent substrate and a plurality of optically reflective regions inclined relative to the optical transparent substrate wave propagation axis. Augmented reality optical apparatus, such a head up display, may include the optical combiner.

TECHNICAL FIELD

Embodiments relate to optical combiner apparatus and components thereof. More particularly but not exclusively, embodiments relate to augmented reality image combiners. Additionally, some embodiments relate to head mounted displays including optical combiners.

BACKGROUND

An optical see through combiner is a fundamental component in an augmented reality display system. The optical combiner enables the real world and an artificially generated scene created by a computer and created by a projector to be optically superimposed.

There are a number of optical systems that have been proposed and adopted with one of the main requirements is to take the projection system away from the eye so it does not obscure the natural view of the world. However, high performance optical combiner systems are complex and difficult to fabricate.

There is a need to provide improved optical combiners that are easier to manufacture and have better performance than current optical systems.

SUMMARY

According to a first aspect, there is provided an optical combiner. The optical combiner may comprise an optically transparent substrate and a patterned region included in the optically transparent substrate and disposed along a wave propagation axis of the substrate. The patterned region may be partially optically reflective and partially optically transparent. The patterned region may comprise a plurality of optically transparent regions of the optically transparent substrate and a plurality of optically reflective regions inclined relative to the optical transparent substrate wave propagation axis.

By including in the optical substrate a patterned region which is partially optically reflective and partially optically transparent, improved optical combiners are provided that are easier to manufacture and have better performance.

According to another aspect, an augmented reality optical combiner is provided. The optical combiner may comprise a transparent optical waveguide substrate for receiving an optical image and viewing there through a distant real world scene and a plurality of reflective elements arranged within the transparent optical waveguide for reflecting the received optical image. The plurality of reflective elements may be arranged in such a way that, when the optical combiner is in use, the received optical image is reflected and superimposed on the real world scene view so as to allow viewing of the distant real world scene while simultaneously viewing the optical image superimposed on the real world scene.

According to yet another aspect, an augmented reality optical apparatus is provided. The augmented reality optical apparatus may comprise a head mounted display and at least one of the aforementioned optical combiners supported on the head mounted display.

According to yet other aspects, methods of combining optical rays are provided. In one aspect, a method of combining optical rays comprises propagating first optical image rays along a length of an optical transparent waveguide substrate towards a pattern region included in said optical transparent substrate; transmitting second optical image rays through a width of the optical waveguide substrate; and selectively reflecting out of said optical substrate said first optical image rays at different points along said substrate from reflective regions of said pattern region; said reflected first optical image rays superimposing on said second optical image rays transmitted out of said optical transparent substrate.

The first optical image rays may be computer generated rays. The second optical image rays may be from a distant real world scene. The pattern region may be a pattern region as set forth hereinbefore.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood, reference will now be made to the accompanying drawings, in which:

FIG. 1 is a front perspective view of an exemplary optical combiner in accordance with an embodiment;

FIG. 2A is a top plan view of an optical combiner in accordance with an embodiment for use with an image projector;

FIG. 2B is a front view of the optical combiner of FIG. 2A;

FIG. 3A is a front view of a sparse aperture reflector in accordance with an embodiment;

FIG. 3B is a side view of the sparse aperture reflector of FIG. 3A;

FIG. 4A is a front view of a sparse aperture reflector in accordance with another embodiment;

FIG. 4B is a side view of the sparse aperture reflector of FIG. 4A;

FIG. 5 is a schematic diagram showing generally how an augmented reality image combiner combines images according to one embodiment;

FIG. 6 is a schematic diagram showing in detail how an augmented reality image combiner combines images according to an embodiment;

FIG. 7 is a front view of augmented reality head mounted display glasses according to an embodiment;

FIG. 8 is a front view of an augmented reality head mounted display helmet according to an embodiment;

FIG. 9 is a front perspective view of an exemplary optical combiner in accordance with another embodiment; and

FIG. 10 is a partial view showing reflective elements of the optical combiner tilted at different angles relative to the common plane in which they are disposed according to one embodiment

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular embodiments, procedures, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details.

Referring now to the accompanying drawings, FIG. 1 shows a front view of an exemplary optical combiner in accordance with an embodiment. Optical combiner 100 is formed from an optically transparent waveguide substrate 105. Substrate 105 has a wave propagation axis 106 extending along a length of the waveguide substrate. Optical image rays entering an optical receiving end or side of substrate 105 propagate through the substrate along the propagation axis 106.

Substrate 105 is a see-through substrate made from optical waveguide substrate material such as but not limited to glass or plastic. Optical rays 150 entering the substrate rear face pass through the substrate material and exit from the substrate front face. An observer located on one side of the substrate and looking through the front face of the substrate can see through the substrate material and observe objects, scenes etc. located on the other side of the substrate.

A patterned region 107 is included in a volume of the optically transparent substrate. Patterned region 107 is partially optically reflective and partially optically transparent. Patterned region 107 comprises a plurality of optically transparent regions 109 of optically transparent substrate 105 and a plurality of optically reflective regions 108 inclined relative to optical transparent substrate wave propagation axis 106. For sake of clarity, not all reflective regions are shown and not all shown reflective regions 108 and transparent regions 109 have been labeled with reference numerals. Optical image rays 140, which are captured in an end of the substrate, propagate along propagation axis 106, pass into patterned region 107, and are selectively reflected at different points along substrate 105 by inclined optical reflective regions 108. The reflected optical image rays 142 exit the front face of substrate 105.

For ease of illustration, rays 140 are shown only as straight through rays. There are countless other rays that bounce along the waveguide rather than passing straight through which are not shown (examples are given in FIGS. 2A, 2B & 6 of a bouncing ray). In some embodiments, patterned region 107 is a regular patterned region. In some other embodiments, pattern region 107 is an irregular patterned region or a combination of a regular pattern region and an irregular patterned region.

The patterned region can take various forms. In some embodiments, optically reflective regions 108 of pattern region 107 are a plurality of optically reflective elements distributed in optically transparent substrate 105, for example as shown in FIG. 1, and optically transparent regions 109 are regions of optical transparent substrate material 105 unoccupied by the plurality of reflective elements. In some other embodiments, pattern region 107 is a reverse design in which and optically transparent regions comprise a plurality of apertures or openings formed in reflective material layer or volume included in the substrate and optically reflective regions comprise the optically reflective material.

In the optical combiner of FIG. 1, optical reflective regions 108 comprise optical reflective elements which are reflective dots. For ease of explanation and visualization, in FIG. 1 and the other accompanying figures, reflective dots are shown enlarged and not to scale. Furthermore, not all reflective dots are shown. In practice, there are for example typically thousands of small reflective dots in the substrate and the dots are small enough that they cannot easily be seen by the human eye so that they do not substantially disrupt the see through performance of the optical combiner. In some embodiments, the optical reflective elements may be other types of discrete reflective elements such as reflective symbols, characters or the like rather than reflective dots.

In some embodiments, each of at least some of the reflective dots or other elements are fully reflective. In some other embodiments, each of at least some of the reflective dots or other reflective elements is partially reflective. For example, at least some of the reflective dots each have reflectivities between 5-100%. In some embodiments, the reflectivites of at least some of the reflective elements are the same. In some embodiments, the reflectivities of at least some of the reflective elements are different.

Optical reflective dots are each made of a reflective material such as but not limited to a single reflective metal layer or multiple layers of reflective oxides or other materials. The reflective dot material may deposited by known deposition techniques. In some embodiments, injection forming with over-molded reflective layers and optical 3D printing, may be used to form the optical substrate including the pattern region. In the embodiment of FIG. 1, reflective dots are distributed in a plurality of distinct planes 115, 120, 125, 130 spaced apart along a length of substrate. Each plane 115, 120, 125, 130, extends between top and bottom sides of substrate 105 and is inclined relative to propagation axis 106 as shown in FIG. 1. Reflective dots in each plane have a regular pattern and shape such as the rectangular matrix of square dots illustrated in FIG. 1. However, in other embodiments, the pattern of reflective dots in one or more of the planes can have other regular shaped matrixes or patterns, or can have an irregular pattern. Furthermore, as will be explained in more detail below, the shape, size, tilt, and/or spacing of each reflective dot, or at least some reflective dots, can be the same or can be different from one another.

Additionally, in some embodiments, reflective dots 108 are distributed in a volume section of the substrate that extends beyond each distinct plane 115, 120, 125, 130. By way of example, FIG. 1 illustrates reflective dots 108 are distributed in the distinct planes 115, 120, 125, 130 and also occupy intermediate regions of the substrate between the planes. In some embodiments of the optical combiner, reflective dots 108 are not distributed in distinct planes but rather are distributed throughout distinct volume sections spaced apart along a length of the waveguide substrate.

In any event, irrespective of how reflective elements are exactly distributed in the different embodiments, the reflective elements can form groups that are spaced along a length of substrate 105. For example, in FIG. 1, a first group 101 of reflective dots is arranged for partially reflecting optical image rays propagating along a length of substrate 105. Reflective elements of subsequent groups 102, 103, 104 spaced apart further along the wave guide are arranged for reflecting optical image rays unreflected by the first group of reflective elements.

Each group of reflective dots distributed about a distinct plane and/or a distinct volume section together with optical transparent substrate gaps therebetween collectively operate as a partially reflective individual reflector. FIG. 1 illustrates four such individual reflectors. However, in other embodiments, the optical combiner may have any number of such reflectors ranging from a single reflector to many many reflectors.

Optical combiner 100 is an extremely simple structure made up of reflective elements rather than reflectors which have a complex set of reflective layers coated over the entire area of each reflector.

Operation of the optical combiner as an optical image combiner is very simple, when the rays that form the image travel along the waveguide substrate some of them hit reflective dots of the first reflector and are re-directed towards the eye. The majority of the rays miss the dots as they only occupy a small area of the first reflector. If for example the dots occupy 5% of the overall area then overall reflectivity is about 5% too and 95% of the image energy passes through to the next reflector and so on. The reflective dots reflect optical rays 140 that have propagated straight through into the substrate but also the other rays 140 that arrive via a wide “bounce” and hit the reflective dots at a glancing angle (see for example the optical combiners shown in FIGS. 2A, 2B & 6 for examples of bouncing oncoming rays and reflections from reflective dots).

In some embodiments, the first reflector (group of dots 101) has a relatively low reflectivity (small area of dots) and subsequent ones have greater reflectivity (bigger area of dots) increasing reflectivity the further along the waveguide substrate. The dot area to optical transparent gap ratio is varied to obtain chosen reflectivity for each reflector.

In yet some other embodiments, all reflective dots 108 are distributed throughout a substrate volume extending along a length of the waveguide rather than occupy distinct planes and/or distinct volume sections. In such embodiments, reflective dots 108 and optically transparent gaps or regions therebetween effectively form one continuous partially reflective reflector extending through the substrate volume. FIG. 9 illustrates one such optical combiner 900 according to an embodiment. Reflective dots 108 are shown distributed throughout a volume of substrate 105. As already mentioned, for ease of illustration not all reflective dots are shown. Furthermore, the specific pattern of dots shown in FIG. 9 is merely an example dot pattern. The reflective dots 108 are still arranged so that the relatively reflectively increases from low to high further along the continuous reflector.

In yet some other embodiments of the optical combiner, the optical substrate is a non see-through substrate.

FIGS. 2A & 2B show the top & front views, respectively, of an optical combiner for use with an optical image generator according to an embodiment. Optical combiner 200 is a slab 205 (flat, parallel sides) of glass or plastic, or other optically transparent waveguide for near eye displays. In alternative embodiments, the waveguide is curved and the faces may not necessarily be parallel. Optical combiner 200 is similar to optical combiner 100 but for ease of fabrication each partially reflective reflector is a sparse aperture reflective surface made up of a surface pattern of the reflective dots or other types of reflective elements. There is an array of four such reflectors 215, 220, 225, 230 shown in FIGS. 2A & 2B but optical combiner 200 can have any number and typically 3 and 6. Reflector 215 has the lowest reflectivity in the array, reflector 220 has the next highest reflectivity, reflector 225 the next highest reflectivity and reflector 240 the highest reflectivity. By way of example, in some embodiments, first reflector 215 has a reflectivity of about 5-7%, second reflector 220 has a reflectivity of about 10%, third reflector 225 has a reflectivity of 20% and fourth reflector 230 with a reflectivity of about 80%.

Sparse aperture surface reflectors 215-230 comprise a plurality of reflective dots (such as dots 108), or other reflective elements, that are formed on a surface and can have many different configurations. In some embodiments, the reflective dots or other elements are arbitrary shapes and are arranged in a matrix on the surface in randomized positions. Reflective dots may be positioned about the surface in a deterministic manner or according to a random function.

In FIGS. 2A & 2B the optical source for generating optical image rays 140 is an image projector 265. A simplified situation is depicted in FIGS. 2A & 2B showing how a single ray 275 originating from the projector 265 is optically coupled into the waveguide substrate 205 using a prism 270. However, other optical coupling methods are possible including direct injection into the end of the waveguide, such as shown in FIG. 1 as rays 140. In other embodiments, other optical generators may be used instead of, or in addition to, projector 265.

One such sparse aperture reflector surface is shown in more detail in FIGS. 3A & 3B, which illustrate a plan view and side view, respectively, of a sparse aperture reflector system according to one embodiment (for use as one or more of the reflectors 215-230 in the optical combiner of FIGS. 2A & 2B). For ease of fabrication, sparse aperture reflector system 330 has a simple matrix 350 of reflective dots 180 or other elements on a regular XY pitch 305. In FIGS. 3A & 3B, reflective matrix 350 is carried on a separate optically transparent substrate which when assembled with the other reflectors forms part of the optical waveguide substrate 205. In some other embodiments, reflective matrix 350 is formed directly on a surface of an intermediate region of the waveguide substrate 205 (see for example intermediate regions of 245-260 of FIGS. 2A & 2B). The height A of sparse aperture reflector surface 330 is typically but not limited to 35-50 mm but will vary depending on the specific optical combiner characteristics desired. The width B of sparse aperture reflector surface is determined according to the number of reflectors required in the optical combiner and according to the thickness of the optical wave guide substrate. The thickness T1 of the reflective dots or other elements will vary but is typically but not limited to 0.1-1 micrometers (um).

FIGS. 4A & 4B illustrate a plan view and side view, respectively, of a sparse aperture reflector system according to another embodiment (for use as one or more of the reflectors 215-230 in the optical combiner of FIGS. 2A & 2B). Sparse aperture reflector system 400 differs from the system 300 in the arrangement and parameters of the reflective dots or other elements. As shown in FIGS. 4A &4B, the reflective dots patterned on the front face of the reflector system have some different shapes. The dot shapes are regular shapes and/or random shapes. By way of example, in FIGS. 4A & 4B, first dot 420 has an arbitrary shape and second dot 415 has an arbitrary shape. Reflective dots have different separation distances. The reflecting dot thickness may also vary for different reflective dots. Optical combiner performance and imaging can be controlled and improved by optimization of various reflector parameters including but not limited to the following: shape of the dots (regular or random shapes), minimum dimension of a dot feature, maximum dimension of a dot feature, degree of randomization over surface, thickness of dot reflecting material, minimum separation between dots, maximum separation between dots and fraction of area occupied by dots. In some embodiments, at least some reflective dots or other elements have a fully or substantially reflective front side and fully or substantially absorbing rear side. As shown in FIGS. 4A & 4B, some reflective dots or elements include a buried relief reflector 460 and a positive relief reflector 455.

In some embodiments of the optical combiners described herein, at least some of the reflective elements 108, etc. in the optical substrate are tilted at different angles from one another and/or at least some of the reflective elements are tilted in parallel with one another. Also, in some further embodiments, some of the reflective elements are individually tilted relative to the planes occupied by the reflective elements. By way of example FIG. 10, is a partial view of the optical combiner showing reflective elements (in this case rectangular reflective dots)1002, 1008 tilted at different angles relative to common plane 1000 in which they are occupied in the optical substrate according to one embodiment. First reflective dot 1002 is tilted in the x axis by a first angle 1004 relative to common plane 1000 whereas second reflective dot 1008 is tilted in the x axis by a second angle 1010 relative to the common plane, the second angle 1010 being different from the first angle 1004. Also, first reflective dot 1002 is tilted in the Z axis by a third angle 1006 relative to common plane 1000 whereas second reflective dot 1008 is titled in the z axis by a fourth angle 1012 relative common plane 1000, the fourth angle 1012 being different from the third angle 1006. In other embodiments, at least some of the reflective elements can be tilted in x, y, z planes (or any combination thereof) differently or in the same way)

The optical combiners of the described embodiments have many advantages over known waveguide reflectors. The optical combiners of embodiments are insensitive to input polarization unlike known combiners that require careful polarization control on transit through the reflectors. The optical combiners of embodiments have inherently broadband optical bandwidth unlike known combiners that require careful design to make sure reflectivity is maintained over a wide range of incidence angles. The optical combiners of embodiments are less complex because patterns of reflective dots or other elements can be fabricated using a single layer of reflective material. In contrast, in known combiners each reflector array will require 20 to 30 separate carefully deposited layers to make one reflecting surface. The optical combiners are easily fabricated and robust compared to known combiners which are difficult to manufacture due to the highly complex multiple layers of reflective films and the fragile nature of the multilayers.

In some aspects, the optical combiners can be used for combining augmented reality images and a real world scenes. As indicated by FIG. 5, an augmented reality image combiner 515 is an optical structure that overlays the real world scene 505 with an optically projected computer generated image 510 and relays the combined image into the eye or eyes 500 of an observer. Optical combiner 515 is any one of the optical combiners described hereinbefore with reference to FIGS. 1-4. The plurality of reflective dots are arranged in such a way that, when the optical combiner is in use, the received computer generated optical image is reflected and superimposed on the real world scene view.

In order to more adequately illustrate how the images are combined in an augmented reality image combiner, reference is made to FIG. 6 which is a simplified schematic of an augmented reality optical combiner system according to an embodiment. This figure demonstrates how an optically projected computer graphic rays contained within the waveguide are relayed into the observer's eye and how rays from the real world scene pass through. Optical combiner 600 can be any one of the optical combiners described hereinbefore with reference to FIGS. 1-4. However, for ease of explanation FIG. 6 has been greatly simplified to show three spaced apart sparse reflectors and show only four reflective dots on each sparse reflector. By way of example, guided rays 620, 625, 630 originating from a projected image 615 are captured in an optical receiving end of the optical waveguide substrate and are relayed towards the observer's eye 605. In particular, example guided ray 620 originating from the projected image 615 captured in the waveguide is relayed towards the observer's eye 605 off a reflective element formed on sparse area reflector n=1 635. Furthermore, example guided ray 625 originating from the projected image 615 and captured in the waveguide passes through transparent region of sparse area reflector 635 and subsequent transparent region of sparse area reflector n=2 640. Yet furthermore, example guided ray 630 originating from the projected image 615 captured in the waveguide is relayed towards the observer's eye 605 off a reflective element formed on sparse area reflector n=2. Arbituray bundle of rays 650 originating from the real scene pass through the optical combiner.

In some aspects, one or more of the optical combiners are incorporated in head mounted displays. In some embodiments, a pair of the optical combiners are included in glasses or Goggle form factor augmented reality head mounted displays. FIG. 7 shows a front view of a pair of the head mounted display glasses according to one embodiment. Glasses or Goggle type head mounted display 700 has a processing module 705 generating computer formed images for binocular view. A left eye optical combiner and projection system 710 and a right eye optical combiner and projection system 715 are included in the head mounted display. The optical combiner in each system 710, 715 is any one of the optical combiners of the embodiments described herein with or without reference to FIGS. 1-6. Optical image projector 265 and optical coupling 270 for example may form part of the projector system. An opto-mechanical frame 720 holds the optical parts securely and in the correct geometric alignment.

In some embodiments, the formed images are for monocular view and only one of the optical combiner and projection systems 710, 715 is included in the head mounted display.

In some embodiments, the head mounted display in which one or more of the optical combiners is incorporated is a helmet form factor augmented reality head mounted display. FIG. 8 shows a front view of a head mounted display helmet according to one embodiment. Helmet head mounted display 800 has a processing module 805 generating computer formed images for binocular view. A left eye optical combiner and projection system 815 and a right eye optical combiner and projection system 820 are included in the head mounted display. The optical combiner in each system 815, 820 is any one of the optical combiners of the embodiments described herein with or without reference to FIGS. 1-6. Optical image projector 265 and optical coupling 270 may for example form part of the projector system. An opto-mechanical sub frame 810 holds the optical parts securely and in the correct geometric alignment. Opto-mechanical sub frame 810 is supported by a mechanically robust shell 835 of the helmet.

In some embodiments, the formed images are for monocular view and only one of the optical combiner and projection systems 815, 820 is included in the head mounted display.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications such as head up type displays. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. For example, the head mounted display sets may be visors, goggles or headband structures and are not limited to the particular types shown in the Figures. Likewise the shape of the optical combiner substrates may be any shape that is capable of guiding and combining images in the manner described hereinbefore.

The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the present disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present disclosure. Exemplary embodiments were chosen and described in order to best explain the principles of the present disclosure and its practical application, and to enable others of ordinary skill in the art to understand the present disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. The descriptions are not intended to limit the scope of the technology to the particular forms set forth herein. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments. It should be understood that the above description is illustrative and not restrictive. To the contrary, the present descriptions are intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the technology as defined by the appended claims and otherwise appreciated by one of ordinary skill in the art. The scope of the technology should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. 

1-40. (canceled)
 41. An augmented reality optical apparatus comprising a head mounted display; and at least one optical combiner supported on said head mounted display, wherein said an optical combiner comprising an optically transparent substrate; and a patterned region included in said optically transparent substrate and disposed along a wave propagation axis of said substrate; wherein said patterned region is partially optically reflective and partially optically transparent; and wherein said patterned region comprises a plurality of optically transparent regions of said optically transparent substrate and a plurality of optically reflective regions inclined relative to said optical transparent substrate wave propagation axis.
 42. The apparatus of claim 41, wherein said patterned region comprises an irregular patterned region.
 43. The apparatus of claim 41, wherein said patterned region comprises a regular patterned region.
 44. The apparatus of claim 41, wherein said patterned region comprises a plurality of optically reflective elements occupying said optically transparent substrate, and optically transparent regions of said optical transparent substrate unoccupied by said plurality of reflective elements.
 45. The apparatus of claim 44, wherein said plurality of optical reflective elements are distributed in a plurality of planes spaced apart along said optical substrate wave propagation axis.
 46. The apparatus of claim 45, wherein said plurality of optical reflective elements are also distributed in a volume of said optical reflective substrate, said volume extending along said optical substrate wave propagation axis.
 47. The apparatus of claim 44, wherein said plurality of optical reflective elements are distributed in volume of said optical reflective substrate, said volume extending along said optical substrate wave propagation axis.
 48. The apparatus of claim 44, further comprise an optical image projector supported on said head mounted display, said optical image projector being in optical communication with said optical waveguide substrate.
 49. The apparatus of claim 44, wherein the plurality of reflective elements comprise a plurality of reflective dots.
 50. The apparatus of claim 44, wherein the plurality of reflective elements comprise reflective elements arranged in at least one regular array.
 51. The apparatus of claim 44, wherein the plurality of reflective elements comprise fully reflective elements.
 52. The apparatus of claim 44, wherein said plurality of reflective elements comprise reflective elements each having a fully or substantially reflective front side and fully or substantially absorbing rear side.
 53. The apparatus claim 44, wherein said plurality of reflective elements comprise reflective elements which are tilted parallel to each other.
 54. The apparatus of claim 53, wherein said parallel tilted reflective elements comprise reflective elements which are distributed in at least one plane which is the same as plane(s) in which the titled reflective elements are distributed.
 55. The apparatus of claim 53, wherein said parallel tilted reflective elements comprise reflective elements which are distributed in at least one plane which is different from the plane(s) in which the titled reflective elements are distributed.
 56. The apparatus of claim 53, wherein said parallel tilted reflective elements are distributed throughout a volume of said optically transparent substrate.
 57. The apparatus of claim 44, wherein said plurality of reflective elements comprise a plurality of groups of said reflective elements, said groups being spaced apart along said waveguide substrate, and wherein a first of said groups of reflective elements is arranged for partially reflecting optical image rays propagating along said propagation axis, and wherein reflective elements of subsequent groups further along said wave guide are arranged for reflecting the optical image rays unreflected by said first group of reflective elements.
 58. The apparatus of claim 44, wherein the size, shape, and spacing there between of the reflective elements is independent from one another.
 59. The apparatus of claim 44, wherein the size, shape, reflectivity, number and/or distribution of said plurality of reflective elements is electronically adjustable to adjust the reflectivity to transmission ratio of the reflector. 